The Internet has become the great political equalizer, giving life this year to insurgent candidates who would never have been able to break through the near-complete control that political parties used to exercise over their nominations.

From Web videos to Internet fundraising to recruiting volunteers, the Internet has helped insurgents knock off incumbents and party-picked candidates in House and Senate races from Alabama to Kentucky to Pennsylvania this midterm season. Tuesday night’s results were expected to include still more surprises for party leaders.

“The D.C. establishment used to serve as the gatekeepers — they had the resources, which meant they had the ability to hand-select the candidate. The Internet has changed that forever,” said David All, president of the David All Group and one of the pioneers on online politicking.

Mr. All founded Slatecard, a Republican-oriented fundraising site that helps small-dollar donors direct their contributions to candidates who share their stances. It follows on the success of ActBlue, a liberal site that says it has raised more than $134 million online from more than 1 million contributions since 2004.

Just as important, platforms such as YouTube have given long-shot candidates ways to circumvent political reporters reluctant to cover campaigns they don’t believe have much chance of success.

TubeMogul, a company that tracks online video hits, found that insurgent candidates have often trounced their establishment-backed opponents on the Web in marquee races.

Most prominent is Florida, where former House Speaker Marco Rubio, a darling of the “tea party” movement, had nearly 20 times the video views in late May as Gov. Charlie Crist, whom Republican leaders had recruited into the race. Mr. Crist has since fled the Republican Party to run as an independent.

Other examples come from both sides of the aisle.

In Pennsylvania, Rep. Joe Sestak had twice as many video views as Sen. Arlen Specter, the Democratic incumbent whom Mr. Sestak ousted in a primary last month; in Alabama, Les Phillip garnered nearly twice as many video views as Rep. Parker Griffith, the incumbent Republican whom Mr. Phillip defeated in a primary; and in Arkansas’ Senate race and a Utah congressional contest, Democratic challengers led incumbents in YouTube views on their way to forcing the incumbents into runoff primaries.

“YouTube tends to favor the underdog in general, but this is even more pronounced than I’ve seen,” said David Burch, director of marketing at TubeMogul. “Once you hit a certain critical mass of views, it’s a great way to spread a message and kick-start a message.”

Internet politics came of age in the 2004 presidential campaign, when former Vermont Gov. Howard Dean attracted followers and raised money online, shaking up the Democratic presidential primary.

Barack Obama, at the time running for a Senate seat in Illinois, took those lessons to new heights four years later, using a multimillion-strong network of online supporters to upset Sen. Hillary Rodham Clinton for the Democratic nomination and then defeat Sen. John McCain in the general election. On the Republican side, meanwhile, Rep. Ron Paul’s “moneybomb” fundraisers brought in millions of dollars and made the Texan a factor to be reckoned with throughout the 2008 primary season.

Mr. Paul’s son, Rand Paul, may be the premier 2010 example of an outsider candidate harnessing the Internet. Powered by tea party supporters and prodigious Internet fundraising, he cruised to a 23-point victory last month in Kentucky’s Republican Senate primary over Trey Grayson, the sitting secretary of state.

Mr. Grayson had the backing of the Senate’s top Republican, Minority Leader Mitch McConnell, also of Kentucky, but that wasn’t enough.

“Rand Paul — if you think back, even as recently as 10 years ago, it would be out of the realm of everyone’s imagination,” said Michael McKenna, a Republican political strategist who has examined how the Internet has affected politics. “What happened between Grayson and Rand Paul is going to become, if not the norm, it’s going to be something you’ll see repeated over and over again.”

Sen. John Cornyn, the Texas Republican and chairman of the National Republican Senatorial Committee who initially backed Mr. Crist, said the Florida governor’s fall within his own party shows the danger of the party establishment trying to pick winners and losers in the midst of surging anti-Washington voter sentiment.

“In this political environment it’s not necessarily helpful for candidates running in states to have the national party chairmen endorse them,” he told reporters earlier this year, even before Mr. Sestak, Mr. Paul and Arkansas Lt. Gov. Bill Halter, who forced Sen. Blanche Lincoln into Tuesday’s Democratic runoff, had their strong showings.

Academics argue that the Internet has returned a certain level of intimacy to campaigning — something Mr. Obama harnessed well in 2008 when his operation had locals e-mailing one another to ask for donations, talk about issues or propose meetings, said Allan Louden, a professor at Wake Forest University who studies political communication.

He said many campaigns are using the Internet to broaden the electorate.

“What’s happening here a lot is that they can get audiences that were unreachable before,” he said.

Mr. McKenna said parties have proved powerless to stop the insurgents, in part because the parties are built around the sort of closed process that the Internet is designed to undermine.

“It used to be when somebody was thinking about running, they would spend an enormous chunk of their time massaging county chairmen, precinct chairmen, all those folks. That’s essentially not necessary anymore — you can build your organization from scratch,” he said.